Make Admin Side Fields Mandatory/Required

To set required fields in woocommerce when adding a product, you will need to use hooks to enforce validation before the product is saved

// Function to validate required fields before saving product
function custom_validate_required_fields( $product_id, $product ) {
    $errors = array();

    // Check if Post Title is empty
    if ( empty( $product->get_title() ) ) {
        $errors[] = __( 'Product title is required.', 'your-text-domain' );
    }

    // Check if Post Content is empty
    if ( empty( $product->get_description() ) ) {
        $errors[] = __( 'Product content is required.', 'your-text-domain' );
    }

    // Check if Featured Image is empty
    if ( ! has_post_thumbnail( $product_id ) ) {
        $errors[] = __( 'Featured image is required.', 'your-text-domain' );
    }

    // If errors found, display error messages and prevent saving product
    if ( ! empty( $errors ) ) {
        foreach ( $errors as $error ) {
            wc_add_notice( $error, 'error' );
        }
        return false; // Prevent saving product
    }

    return true; // Proceed with saving product
}
add_action( 'woocommerce_process_product_meta', 'custom_validate_required_fields', 10, 2 );

woocommerce_process_product_meta hook fired when a product is being saved. It checks if the required fields Post Title, Post Content, and Featured Image are empty